Apparatus for completing a subterranean well and method of using same

ABSTRACT

In completing a well bore in a underground formation, the well bore being closed off by a closing structure for blocking flow of pressurized fluid through the well bore, a substantially tubular element having a tube wall surrounding an axial bore is passed through the closing structure. The tube wall having passed the closing structure is processed along at least a portion of its axial dimension from a first condition into a second, processed condition. In the first condition, the tube wall is substantially impermeable in radial direction to pressurized fluid for precluding a flow of pressurized fluid from passing the penetrated closing structure. In the second condition the tube wall is radially permeable to pressurized fluid along at least a processed portion of its axial dimension. A tubular element to be used in such an application is described as well.

BACKGROUND OF THE INVENTION

The invention relates to a method for completing a well bore in anunderground formation, said well bore being closed off by a closingstructure for blocking flow of pressurized fluid through said well bore,comprising the step of passing a substantially tubular element having atube wall surrounding an axial bore through said closing structure.

Such a method is known from practice and is carried out in the course ofthe completion of a well, i.e. the finalizing operations for making awell bore ready for functions such as producing oil, gas or anotherfluid from the formation, reservoir observation or fluid injection.

However, in badly consolidated or fractured formations these functionscan be hampered by inflow of particles into the well bore. Suchparticles can originate either from the formation itself or fromproppant materials used to support the completion, i.e. the section ofthe well bore that is to perform the above-mentioned function. Such aparticle inflow does not only further destabilise the formation, but canalso block the well bore or may entail the need of separating theparticles from fluid produced by the well bore.

To overcome this problem, it has been proposed to support the productionsection using a supporting device to support the formation and anyproppant used for completing the well.

From U.S. Pat. No. 5,366,012, it is known to install a slotted tube assupporting device. The slotted tube is radially expanded to support theformation and/or proppant material. This is carried out when the slottedtube is located at an uncased bottom section of the borehole, andinvolves axially forcing a mandrel through the slotted tube to make itexpand radially.

In practice, as part of the completion operation, after the well borehas been provided with a casing and a closing structure, such as ablow-out preventer, a production string carrying the slotted tube ispassed through the closing structure.

However, since supporting devices such as slotted tubes are providedwith penetrations, to be able to safely pass the supporting devicethrough the closing structure, it is necessary to “kill” the well, bybalancing the upward pressure of e.g. oil or gas in the formation with afluid column in the well bore to avoid fluid flow from the well via thepenetrations in the wall of the supporting device.

However, balancing a well is a time consuming operation which may alsodamage the formation and/or leave the well in an unsafe, uncontrollablecondition.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a solution which allows thecompletion of an uncased section of a borehole, without having tobalance the well.

According to one aspect of the present invention, this object isachieved by carrying out a method of completing a borehole in accordancewith claim 1.

This way, pressurised fluid in the well is substantially prevented frompassing the penetrated closing structure, because the tube wall which isto complete the uncased section is impermeable to any pressurized fluidin the well as it penetrates and passes through the closing structure.Portions of the tube wall having been brought in position or having atleast passed the closing structure are made permeable, so that fluid canbe received via the initially impermeable tube wall.

According to a further aspect of the invention, a pressurized drillingfluid is axially fed through said tubular element before said processingis carried out. This way, the drilling fluid can be used to power thedrill and does not prematurely radially exit the tubular element throughthe circumferential openings.

According to another aspect of the present invention, theabove-mentioned object is achieved by providing a tubular element inaccordance with claim 10.

This tubular element can be passed through a closing structure forblocking a flow of pressurised fluid through a well bore, while apressure drop over the closing structure exists without allowing fluidto the closing structure via the bore of the tubular element. In itsproduction position, the tubular element can be made permeable to allowthe fluid to be obtained from the well to pass into the productionstring via the tubular element.

Particular embodiments of the method and of the tubular elementaccording to the invention are set forth in the dependent claims.

Further objects, features, advantages and details of the invention aredescribed with reference to embodiments shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a cross-section of a well bore having ablow-out preventer as a closing structure being passed by a tubularelement in first condition;

FIG. 1A shows an alternative embodiment of the tubular element of FIG.1;

FIG. 2 shows the well bore of FIG. 1 with the tubular element in firstcondition being located in an uncased production zone;

FIG. 3 shows schematically a partial cross-section of a tubular elementin a first condition in an uncased production zone of a bore hole;

FIG. 4 shows schematically a cross-section of a tubular element in asecond condition in a production section of a bore hole;

FIG. 5 shows schematically a cross-section of another well bore having acemented casing shoe as a closing structure being penetrated by anothertubular element in a first condition; and

FIG. 6 shows a cross-sectional view of a wall portion of a still anothertubular element.

DETAILED DESCRIPTION

To enhance clarity, in the drawings, the radial dimensions have beendrawn on an enlarged scale relative to the axial dimensions.

FIGS. 1 and 2 show a well bore 1 in an underground formation 2. Theunderground formation 2 has a production zone 2A which may be badlyconsolidated, fractured or otherwise instable. The well bore 1 is closedoff by a closing structure 3 preventing pressurized fluid from flowingup through the well bore 1. The well bore 1 has a casing 4 which issealed to the formation by a layer of cement 5.

The well bore 1 comprises a cemented casing shoe 6 through which a hole7 has been drilled into the production zone 2A, of the formation. Theclosing structure 3 is a conventional blow-out preventer system or arotating preventer system. The closing structure 3 carries a packer 8for sealing a tubing 9 passing therethrough. Such blow-out preventersare well known to those skilled in the art. In underbalanced condition,a relatively large pressure difference of 350 to 500 bar can be presentbetween the faces A and B of the blow-out preventer.

As is shown in FIG. 1, a tubular element 10 having a tube wall section11 surrounding an axial bore 12 is passed through an opening in theblow-out preventer 3. The tubular element 10 is in a first condition inwhich it is impermeable to pressurized fluid in radial direction andable to withstand a pressure of up to at least 50 bar and preferably atleast the pressure rating of the preventer system.

The tubular element 10 has a tube wall section 11 which is weakened atcircumferentially and axially distributed locations and composed of atubular body 13 having a plurality of openings 14 and a cover layer 15on the outer circumference of the tubular body 13, covering the openings14. The tubular element 10 is sealed off at its bottom end by a mandrel17.

When passing the blow-out preventer 3 while in a first condition, thetubular element 10 behaves essentially like a normal tubing sectionpassing the blow-out preventer. Hence, when passing the blow-outpreventer, the risk of a blow-out caused by underbalance is greatlyreduced and unintended flow of pressurized fluid past the penetratedclosing structure is prevented. Therefore, there is no need to preciselybalance the well pressure. Accordingly, the risk of overbalancing thewell and thereby damaging the well is substantially reduced and, inaddition, time is saved.

When the tubular element 10 has passed through the closing structure 3it is passed coaxially through the casing 4 while suspended from atransport tube 9 sealingly connected to the tubular element 10.

After the tubular element 10 has been positioned in an uncasedproduction zone 20 of the well bore 1, the tube wall 11 is expandedalong a major portion of its length, starting from a situation as shownin FIG. 3 to a situation as shown in FIG. 4. In the present example,this is carried out by axially retracting a mandrel 17 through the axialbore 12 of the tubular element 10. Thus, the tubular body is radiallyexpanded as the mandrel 17 is passed through. By radially expanding thetubular element to its second condition, additional support of the oilproducing formation 2A is provided by the expanded tube wall.

An alternative embodiment is shown in FIG. 1A. In this embodiment,radial expansion of the tube wall can be carried out by forcing anexpander unit 17A downward through the tubular element 10. The bottom ofthe tubular element is closed off by a closing device, e.g. combinedwith a washing or drilling device 17B.

For suitable expansion methods, which are known as such, reference ismade to U.S. Pat. No. 5,306,012. In particular, the mandrel 17 can be ofa collapsible type, such that it can be inserted and retracted throughthe tubing 9 in collapsed condition. The mandrel 17 is suspended from arod 18, which is also used to lower the mandrel and to pull the mandrelup.

Upon radial extension of the tubular body 13, the layer 15, which issubstantially inextensible, is severed particularly at the locations ofthe holes 14 and becomes permeable in at least these locations. Due tothe permeability, the pressure difference over the tube wall in thefirst condition is much lower than the pressure difference in the secondcondition. Oil and gas can now flow from the production zone 2A throughthe tubular element 10 into the tubing 9 and upwards through the tubing9 under control of control valves above the well in the first condition.The pressure on the tube wall can e.g. be 350 to 1000 Bar higher than inthe second condition.

FIG. 5 illustrates another, presently most preferred method ofcompleting a well bore 101. In this case, the well bore 101 has aclosing structure 103 at the top and a cemented casing shoe 106 at thebottom of the well bore 101. As in the previous example, boring the wellbore 1 and providing it with a cemented casing 4 can be performed usingtechniques well known to those skilled in the art.

When the production zone 120 is to be drilled, a hole 107 is drilledthrough the casing shoe 106 and then the production zone 120 itself isdrilled in the production formation 102A beyond the casing shoe 106.During drilling, the drill string is rotated around its longitudinalaxis, as indicated with arrow 125.

During drilling, pressurized drilling fluid is fed axially through thetubular element 110, e.g. through the axial bore 112 and exits the drillstring through or near the drill bit 122. The tubular element is in thefirst condition and hence radially impermeable to the pressurizeddrilling fluid. This way, the drilling fluid does not exit the tubularelement prematurely and can be used to power the drill and to wash awaycuttings. The hole is drilled to total depth using the blow outpreventer system on the surface to control the flow from the well.

After the tubular element 110 has been drilled sufficiently deep intothe oil producing zone 102A and the tubular element 110 has reached thedesired location in the production zone 120, the drill bit 122 isaxially retracted through the bore 112 in the tubular element 110, i.e.in the direction of arrow 124.

This way, the tube wall 111 is radially expanded into its secondcondition. While being expanded, the tube wall 111 becomes radiallypermeable to pressurized fluid along the expanded portion of its length.Now, oil or gas can be produced from the production zone 102A. Theexpanding operation can be performed using an expander unit formed by orcombined with the drill bit and a bottom hole assembly or with any othersuitable expansion means

Since in this mode of carrying out a method according to the invention,the drilling of at least a portion of the well bore is carried out usinga drill string including the tubular element to be made permeable afterreaching its production position, the time needed to prepare theproduction ready well bore is substantially reduced, because theoperation of inserting the completion into the well bore is performedsimultaneously with the operation of inserting the drill string into thewell bore. Furthermore, because the tubular element can be expandeddirectly after the drilling operations, compared to having to retreivethe tubular element and subsequently insert a supporting device, thechance of collapse of the borehole is greatly reduced and time is saved.

The tubular element 110 has a tube wall 111 provided withcircumferentially and axially distributed openings 114. The openings areprovided in a tubular body 113 which is covered by an outer layer 115Aand an inner layer 115B of material. In its first condition, the tubularelement 110 is impermeable to pressurized fluid and substantiallyinextensible. The layers 115A and 115B comprise a resinous material,such that upon radial expansion of the tube wall 111 of the tubularelement 110, the layers 115A and 115B are severed and do not cover theopenings 114 anymore, such that the tube wall 111 becomes radiallypermeable to pressurized fluid. Preferably, the layers 115A and 115Bcomprise a material that sticks to the tubular body 113 in the secondcondition to prevent soiling of the production zone 102A and of producedgas, oil or other produced fluids by foreign particles originating fromthe layers 115A and 115B.

The layers 115A and 115B each substantially enhance torsion stiffness ofthe tubular element 110, in particular if fibres in the layers 115Aand/or 115B are laid-up in a torsion-resistant diagonally woundconfiguration. Thus, even though a large number of openings or otherwiseweakened locations are provided in order to be opened upon expansion, itis nevertheless possible to use the tubular element 110 to transfer thesubstantial torque of typically up to 5000 to 25000 lbs required in adrilling operation.

The layers 115A and 115B comprise reinforcing fibres, preferably glass,carbon or other fibres embedded in a resinous matrix material. Thefibres can be knitted, braided or wound to enhance the strength of thelayer.

These constructional features contribute to providing a layer 115A or115B that is sufficiently impermeable to pressurized fluid, sufficientlytorsion resistant and that does not disintegrate upon expansion of thetubular element 110, so that the formation of loose particles is kept toa minimum.

Since the layers 15 in FIGS. 1-3 and 115A in FIG. 5 are located on theoutside of the respective tubular bodies 13, 113, the tubular elements10, 110 in the first condition have a particularly high resistance toexternal pressure. This is advantageous in situations in which thepressure on the outside of the tubular element 10, 110 is greater thanthe pressure on the inside of the tubular element 10, 110, e.g. when thewell is underbalanced relative to the pressure in the production zone2A, 102A.

The layer 115B in FIG. 5 on the inside of the tube body 113 provides aparticularly high resistance against pressure from the inside of thetubular element 110, this occurs for instance when drilling fluid issupplied through the tubular element.

The layers 15, 115A and 115B can also serve to protect an additionalstructure interposed between the layer and the tubular body 13.

FIG. 6 shows a build-up of layers in which an expandable screen 223 isinterposed between an inner layer 215B of sealing material and an outerlayer 215A of sealing material and to the outside of a tube body 213.

By providing that the screen is covered by a layer of sealing material,the expandable screen 223 is protected. The outer layer 215A forinstance, protects the screen while the tubular element 210 is insertedinto the casing. The inner layer 15A can serve to protect the screen 213from being soiled or even clogged via the openings 14 by particles inthe drilling fluid (mud). The reinforcing fibres in the matrix material230 are shown as dots 232 and are indicated with reference numeral 231.

Although the invention has been described in detail with reference to apreferred embodiment, from the foregoing it will readily become apparentto those skilled in the art that many and varied changes can be madewithout departing from the spirit and scope of the invention.

For example, the tube wall can also be brought from the first conditioninto the second condition without radial expansion, e.g. by rotating ortelescoping movement of two tubular bodies relative to each other, suchthat a number of holes are closed off in the first condition and areopened by alignment in the second condition. Furthermore, the tube wallsection can be weakened in other ways, e.g. by recesses of which thematerial with decreased thickness is severed upon expansion, by barrelstaves that overlap or that are adjacent in the first condition and thatare interposed in the second condition. In addition, radial expansionusing a mandrel can also be carried out by axially forcing the mandrelthrough the tubular element downwardly, i.e from top to bottom. Also,the production section can be located horizontally in the oil producingzone 2A. Such embodiments are readily available to the man skilled inthe art and are within the scope of the following claims.

What is claimed is:
 1. A method for completing a well bore in anunderground formation, said well bore being closed off by a closingstructure for blocking flow of pressurized fluid through said well bore,comprising the steps of: a) passing a substantially tubular elementhaving a tube wall surrounding an axial bore through said closingstructure; and b) processing said tube wall along at least a portion ofits axial dimension having passed said closing structure from a firstcondition into a second, expanded condition; said tube wall in saidfirst condition being substantially impermeable in radial direction topressurized fluid for preventing pressurized fluid from passing saidclosing structure and said tube wall in said second expanded conditionbeing radially permeable to pressurized fluid along at least theprocessed portion.
 2. Method according to claim 1, wherein saidprocessing of said tube wall involves expanding in at least a radialdirection.
 3. A method according to claim 1, wherein a first pressuredifference is present over said tube wall in said first condition and asecond pressure difference is present over said tube wall in said secondcondition, said first pressure difference being substantially largerthan said second pressure difference.
 4. A method according to claim 1,wherein said well bore comprises a casing and said tubular element iscoaxially inserted within said casing using a transport tube carryingsaid tubular element.
 5. A method according to claim 1, wherein saidprocessing is carried out while said tube wall is located in an uncasedproduction zone of said well bore.
 6. A method according to claim 1,wherein, before said processing is carried out, a pressurized drillingfluid is axially fed through said tubular element.
 7. A method accordingto claim 1, wherein, before said processing is carried out, drilling ofat least a portion of said well bore is carried out using a drill stringincluding said tubular element.
 8. A method according to claim 1,wherein said closing structure is provided in the form of a cementedcasing shoe at a bottom section of said well bore, further including thesteps of drilling through said casing shoe and drilling into saidunderground formation beyond said closing structure to provide anuncased production zone of said well bore.
 9. A method according toclaim 1, wherein during or after said step of processing said tube wallalong at least a portion of its axial dimension, a drilling element isaxially retracted through said tube wall.
 10. A tubular element forlining an uncased production zone of a well bore in an undergroundformation, said tubular element having a tube wall section surroundingan axial bore and being processable over at least a portion of its axialdimension from a first condition into a second, expanded condition, saidtube wall in said first condition being impermeable to pressurized fluidand said tube wall in said second expanded condition being radiallypermeable in at least said processed portion to pressurized fluid.
 11. Atubular element according to claim 10, wherein said processed portion insaid second condition has an expanded cross sectional area surrounded byits external surface and a basic cross sectional area surrounded by itsexternal surface in said first condition, said expanded cross sectionalarea being larger than said basic cross sectional area.
 12. A tubularelement according to claim 10, wherein said tube wall section in saidfirst condition comprises a tubular body having a plurality ofpenetrations and at least one layer covering said penetrations,impermeable to pressurized fluid and substantially inextensible, andwherein, in said second condition, said layer is severed and permeableto pressurized fluid over at least a portion of the axial dimension ofsaid tube wall section.
 13. A tubular element according to claim 12, inwhich said layer comprises a resinous material.
 14. A tubular elementaccording to, claim 12, in which said layer comprises fibres.
 15. Atubular element according to claim 14, in which said fibres form aknitted, braided or wound structure.
 16. A tubular element accordingclaim 12, in which said layer is a composite structure including fibresembedded in a matrix material.
 17. A tubular element according claim 12,in which at least in said second condition said layer or said sealingmaterial at least substantially adheres to said tubular body.
 18. Atubular element according to claim 10, in which said tube wall in saidfirst condition comprises a tubular body having a plurality ofpenetrations and sealing material sealing off said penetrations, saidsealing material being located at least on the outside of said tubularbody.
 19. A tubular element according to claim 18, in which said tubewall in said first condition comprises a tubular body having a pluralityof penetrations and sealing material sealing off said penetrations, saidsealing material being located at least on the inside of said tubularbody.
 20. A tubular element according to claim 19, in which, in saidfirst condition, an additional structure is interposed between an innerlayer of sealing material and an outer layer of sealing material.
 21. Atubular element according to claim 20, in which said additionalstructure is an expandable screen, protected by said layers of sealingmaterial in said first condition.
 22. A method for completing a wellbore in an underground formation, the method comprising: passing asubstantially tubular element through a closing structure for blockingflow of pressurized fluid through the well bore, the tubular elementcomprising: a tube wall surrounding an axial bore and having severedlocations disposed along its length; and an impermeable covering layerblocking flow through the severed locations; and processing at least aportion of the tube wall to open the impermeable covering layer and toenlarge the severed locations into holes, such that the tubular elementis converted to a second, permeable state.